Slotted cathode structure



y 1949. 4 B. J. BUTLER 2,468,736

SLOTTED CATHODE STRUCTURE Filed June 13, 1946 /NVENTO/? BENJAMIN J. BUTL El? BY I f Patented May 3, 1949 UNITED STATES PATENT OFFICE 2 Claims.

This invention is directed to the construction of electrodes, and more particularly directly heated cathodes for use in very high-level poweroutput electron-discharge devices.

Experience has shown thatsuch cathodes which comprise long lengths of wire may either bow or buckle .at operating temperature and that it is not feasible in high powered tubes to use insulating material to brace the cathodes because of the severe voltage and temperature conditions encountered. It would likewise be highly undesirable to stiffen said cathodes by increasing their thickness because of the increased heating current, and because of the reduced effective cathode emitting area of larger cross-sections for a given cathode power.

Cathodes in the form of coils, although providing a higher resistance to the flow of current because of such configuration, tend to sag under their own weight, especially when raised to temperatures used in the operation of power-output electron-discharge devices in the range above ten kilowatts. The sagging of the coiled cathode causes adjacent turns to touch with a consequent reduction of resistance and resulting rise in current culminating in the destruction of the cathode.

Since the poweroutput is dependent on the area of the cathode, and other electrical characteristics of the device limit the cross-section, it is evident as the power is increased that the length of the cathode must be increased, and to ofiset turbulence and oscillatory action in the emitting member, a very sturdy structure must be provided to realize the highest efl'iciency from such a device.

It is, therefore, a main object of the present invention to provide a device of the type described which will produce a greater emission for a given power input than cathodes heretofore available;

Another object of the present invention is to produce a device of the type described capable of extremely large power output at ultra-high frequencies.

A furtherobject of the present invention is to provide a novel improved cathode structure.

These and other objects will become apparent as the description of the device of the present invention progresses and is illustrated by the attached drawing in which:

Fig. 1 is a partial fragmentary view of an electron-discharge device, such as a magnetron, employing the device of the present invention;

Fig. 2 is an illustration of the device showing an end view and elevation of same; and

Fig. 3 is an unfolded view of the device of the present invention.

2 Although the illustrations hereinbefore described show the use of the device in connection with a magnetron type of electron-discharge device, it is equally applicable to other types where the main object is extremely large power output.

Referrin more particularly to Fig. 1, the device of the present invention, in one embodiment, is a hollow metal cathode l9. Said cathode is supported between two metal shield members H and E2. The shield members and cathode mat be composed of tungsten or the like.

Shield member ll threadedly engages cathode heater lead l3 which is disposed within the cathode. Shield member I2 threadedly engages a second cathode heater lead Hi.

In assembling the cathode, in this particular embodiment, two shoulders 15 and I5 abut the ends of cathode it and two annular ribs ll and I8 extend within the open ends of said cathode. The shoulders provide a suitable surface adjacent the cathode Ill for welding said cathode at points 1.9 and 2d securely to the shield members it and 12. The annular ribs ll and i8 prevent displacement of the cathode from its predetermined position between the shield members H and I2. It was found desirable, in order to prevent undue expansion of the cathode it) when welding same in position, to place a ring clamp (not shown) around said cathode.

The assembly above described is disposed, in the present embodiment, between the paddles 2| and 22 as practiced in the art of magnetron construction, the shields H and I2 confining the electrons within the space bounded by members H, 12, 2!, and 22.

The assembly comprising cathode l9, shield members H and 12, cathode heater leads l3 and I4 is supported Within the discharge device in the following manner. Heater lead i3 is attached to a metal ferrule 23, by welding, brazing or other suitable means, said ferrule in turn being attached to a metal tubular member 24 by a glass-to-metal seal 25 which electrically insulates member 23 from 24. An iron-cobalt-nickel alloy havin the same coeflicient of expansion as glass is the preferred material for members 23 and 24. Member 24 is securely attached to the second heater lead [4 by weldin or the like and said lead is firmly attached, in a like manner, to a second metal ferrule 25. The last-named ferrule is in turn attached to a second metal tubular member 21 through the medium of a second glass-to-metal seal 28, said seal electrically insulating ferrule 26 from tubular member 21. Members 26 and 21 may be made of an iron-cobaltmickel alloy having the same coefficient of expansion as glass, or other like alloy.

Tubular member 21 is rigidly attached within aperture 36 in flat metal annular member 29 by welding or other suitable means. A portion of aperture 36 is made appreciably larger in diameter to accommodate said tubular member 21. Annular member 29 is then secured to anode 3| by brazing, welding or other suitable means.

As above described, the arrangement and cooperation of the cathode and its supporting member provide a unitary assembly which can be' readily positioned within a discharge device. The arrangement likewise provides an assembly which may be readily removed should the cathode be impaired and. it is necessary to renew same. There are many methods known in the art for attaching the aforesaid assembly so that same may be readily removed and a discussion of these methods is therefore believed unnecessary in the present description of the device of this invention.

Fig. 2 illustrates an end View and a view in elevation of the device as used in the particular embodiment under discussion. The end view indicates that the cathode I8 is a substantially hollow member, the longitudinal slot 32 being formed by omitting the operation of welding said cathode into a completely continuous hollow member, said omission thus saving one operation in constructing the device. If desired said member may be so welded, as either method will Work equally well.

After the operation of rolling member I B into a substantially hollow form, a plurality of substantially parallel slots 33, disposed at right angles to the longitudinal axis of said hollow member, are cut into the surface thereof, for example, by grinding, The slots are disposed with respect to each other, so that each alternate slot 3 overlaps the juxtaposed ends 35 and 3B of the adjacent slots. This novel arrangement provides a plurality of electrically conductive curved paths for the flow of current through the solid material of said member from one end to the other end thereof. The curved paths so provided appreciably increase the resistance of member I0, resuit in a comparatively lower consumption of current and provide a large area for the copious emission of electrons.

The advantage of this novel type of cathode construction over coil and rod type cathodes is readily apparent. Such construction provides a rigid seli-supporting structure, easily mounted. It eliminates the use of tensioning means to prevent sagging of same when subjected to the extreme temperatures used in the operation of power tubes with output of the order of about ten to twenty-five kilowatts. As a result of the aforemention d features, the life of such a cathode far exceeds that of conventional cathodes now in use.

Fig. 3 illustrates the form of the cathode when unrolled. In this form the slots 33 may be punched out and the flat member then rolled into the form illustrated in Fig, 2. The series of arrowheads 3'! illustrates one of the tortuous paths of current flow which this novel form of cathode construction provides. It is readily evident that such a path provides appreciable resistance.

While but one embodiment of the device of the present invention has been described hereinbefore, said device is applicable to any type of electron-discharge or gaseous conduction tube where power output requirements are extremely high.

Therefore, it is to be understood that many modifications are possible without departing from the true spirit and scope of the present invention.

What is claimed is:

1. A cathode, comprising a hollow substantially cylindrical metal member having a plurality of substantially parallel slots in the surface thereof, said slots extending transversely to the axis of said member, said slots being arranged in a plurality of rows spaced longitudinally with respect to said axis with each row being constituted by a plurality of circumferentially-spaced slots, and a substantially stifi low resistance rod axially disposed within said hollow member and rigidly connected electrically and mechanically to one end thereof.

2. A cathode, comprising a hollow substantially cylindrical metal member having a plurality of substantially parallel slots in the surface thereof, said slots extending transversely to the axis of said member, said slots being arranged in a plurality of rows equidistantly spaced longitudinally with respect to said axis with each row being constituted by a plurality of equidistantly circumferentially-spaced slots, the slots in each alternate row overlapping the juxtaposed ends of the slots in the rows next adjacent thereto and defining a plurality of electrically-conductive paths between the ends of said hollow member substantially longer than the distance between said ends, and a substantially stifi low resistance rod axially disposed within said hollow member and rigidly connected electrically and mechanically to one end thereof.

BENJAMIN J. BUTLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Murdock May 7,1946 

